Alzheimer disease: new concepts on its neurobiology and the clinical role imaging will play

The ENIGMA Consortium: large-scale collaborative analyses of neuroimaging and genetic data

The Enhancing NeuroImaging Genetics through Meta-Analysis (ENIGMA) Consortium is a collaborative network of researchers working together on a range of large-scale studies that integrate data from 70 institutions worldwide. Organized into Working Groups that tackle questions in neuroscience, genetics, and medicine, ENIGMA studies have analyzed neuroimaging data from over 12,826 subjects. In addition, data from 12,171 individuals were provided by the CHARGE consortium for replication of findings, in a total of 24,997 subjects. By meta-analyzing results from many sites, ENIGMA has detected factors that affect the brain that no individual site could detect on its own, and that require larger numbers of subjects than any individual neuroimaging study has currently collected. ENIGMA's first project was a genome-wide association study identifying common variants in the genome associated with hippocampal volume or intracranial volume. Continuing work is exploring genetic associations with subcortical volumes (ENIGMA2) and white matter microstructure (ENIGMA-DTI). Working groups also focus on understanding how schizophrenia, bipolar illness, major depression and attention deficit/hyperactivity disorder (ADHD) affect the brain. We review the current progress of the ENIGMA Consortium, along with challenges and unexpected discoveries made on the way.

Brain investigation and brain conceptualization

The brain of a patient with Alzheimer's disease (AD) undergoes changes starting many years before the development of the first clinical symptoms. The recent availability of large prospective datasets makes it possible to create sophisticated brain models of healthy subjects and patients with AD, showing pathophysiological changes occurring over time. However, these models are still inadequate; representations are mainly single-scale and they do not account for the complexity and interdependence of brain changes. Brain changes in AD patients occur at different levels and for different reasons: at the molecular level, changes are due to amyloid deposition; at cellular level, to loss of neuron synapses, and at tissue level, to connectivity disruption. All cause extensive atrophy of the whole brain organ. Initiatives aiming to model the whole human brain have been launched in Europe and the US with the goal of reducing the burden of brain diseases. In this work, we describe a new approach to earlier diagnosis based on a multimodal and multiscale brain concept, built upon existing and well-characterized single modalities.

Physical activity reduces hippocampal atrophy in elders at genetic risk for Alzheimer's disease

We examined the impact of physical activity (PA) on longitudinal change in hippocampal volume in cognitively intact older adults at varying genetic risk for the sporadic form of Alzheimer's disease (AD). Hippocampal volume was measured from structural magnetic resonance imaging (MRI) scans administered at baseline and at an 18-month follow-up in 97 healthy, cognitively intact older adults. Participants were classified as High or Low PA based on a self-report questionnaire of frequency and intensity of exercise. Risk status was defined by the presence or absence of the apolipoprotein E-epsilon 4 (APOE-ε4) allele. Four subgroups were studied: Low Risk/High PA (n = 24), Low Risk/Low PA (n = 34), High Risk/High PA (n = 22), and High Risk/Low PA (n = 17). Over the 18 month follow-up interval, hippocampal volume decreased by 3% in the High Risk/Low PA group, but remained stable in the three remaining groups. No main effects or interactions between genetic risk and PA were observed in control brain regions, including the caudate, amygdala, thalamus, pre-central gyrus, caudal middle frontal gyrus, cortical white matter (WM), and total gray matter (GM). These findings suggest that PA may help to preserve hippocampal volume in individuals at increased genetic risk for AD. The protective effects of PA on hippocampal atrophy were not observed in individuals at low risk for AD. These data suggest that individuals at genetic risk for AD should be targeted for increased levels of PA as a means of reducing atrophy in a brain region critical for the formation of episodic memories.

RBANS memory indices are related to medial temporal lobe volumetrics in healthy older adults and those with mild cognitive impairment

The current study (i) determined whether NeuroQuant(®) volumetrics are reflective of differences in medial temporal lobe (MTL) volumes between healthy older adults and those with mild cognitive impairment (MCI) and (ii) examined the relationship between RBANS indices and MTL volumes. Forty-three healthy older adults and 57 MCI patients completed the RBANS and underwent structural MRI. Hippocampal and inferior lateral ventricle (ILV) volumes were obtained using NeuroQuant(®). Results revealed significantly smaller hippocampal and larger ILV volumes in MCI patients. MTL volumes were significantly related to the RBANS Immediate and Delayed Memory and Language indices but not the Attention or Visuoconstruction indices; findings that demonstrate anatomical specificity. Following discriminant function analysis, we calculated a cutpoint that may prove clinically useful for integrating MTL volumes into the diagnosis of MCI. These findings demonstrate the potential clinical utility of NeuroQuant(®) and are the first to document the relationship between RBANS indices and MTL volumes.

Dementia and mild cognitive impairment in adults with intellectual disability: issues of diagnosis

Individuals with intellectual disability (ID) are now living longer with the majority of individuals reaching middle and even "old age." As a consequence of this extended longevity they are vulnerable to the same age-associated health problems as elderly adults in the general population without ID. This includes dementia, a general term referring to a variety of diseases and conditions causing substantial loss of cognitive ability and functional declines; adults with Down syndrome are at especially high risk. A great deal of recent effort has focused on the very earliest detectable indicators of decline (and even prodromal stages of dementia-causing diseases). A condition called mild cognitive impairment (MCI) has been conceptually defined as a decline in functioning that is more severe than expected with typical brain aging but not severe enough to meet criteria for a diagnosis of dementia. Consensus criteria for both dementia and MCI have been developed for typically developing adults but are of limited applicability for adults with ID, given their pre-existing cognitive impairments. Early diagnosis will continue to be of growing importance, both to support symptomatic treatment and to prevent irreversible neuropathology when interventions are developed to slow or halt the progression of underlying disease. While the intellectual and developmental disabilities field has for some time recognized the need to develop best-practices for the diagnosis of MCI and dementia, there remains a pressing need for empirically based assessment methods and classification criteria.

Genetics of Alzheimer disease

Alzheimer disease prevails as a major cause of disability in the elderly population and ranks as the most common form of dementia that affects 1 of 8 individuals older than 65 years of age. Most AD cases are late in onset and are probably influenced by both genetic and environmental factors. Apart from age, the risk factors include family history; brain injury, both traumatic and vascular; and metabolic diseases, such as diabetes, hypercholesterolemia, and obesity. Based on twin studies, inheritance plays a role in approximately 80% of cases (familial and sporadic).

Paraoxonase 1 in neurological disorders

Paroxonase 1 displays multiple physiological activities that position it as a putative player in the pathogenesis of neurological disorders. Here we reviewed the literature focusing on the role of paraoxonase 1 (PON1) as a factor in the risk of stroke and the major neurodegenerative diseases. PON1 activity is reduced in stroke patients, which significantly correlates inversely with carotid and cerebral atherosclerosis. The presence of the R allele of the Q192R PON1 polymorphism seems to potentiate this risk for stroke. PON1 exerts peroxidase activities that may be important in neurodegenerative disorders associated with oxidative stress. PON1 is also a key detoxifier of organophosphates and organophosphate exposure has been linked to the development of neurological disorders in which acetylcholine plays a significant role. In Parkinson's disease most of the studies suggest no participation of either L55M or the Q192R polymorphisms in its pathogenesis. However, many studies suggest that the MM55 PON1 genotype is associated with a higher risk for Parkinson's disease in individuals exposed to organophosphates. In Alzheimer's disease most studies have failed to find any association between PON1 polymorphisms and the development of the disease. Some studies show that PON1 activity is decreased in patients with Alzheimer's disease or other dementias, suggesting a possible protective role of PON1. No links between PON1 polymorphisms or activity have been found in other neurodegenerative diseases such as multiple sclerosis and amyotrophic lateral sclerosis. PON1 is a potential player in the pathogenesis of several neurological disorders. More research is warranted to ascertain the precise pathogenic links and the prognostic value of its measurement in neurological patients.

Neuroimaging of rapidly progressive dementias, part 1: neurodegenerative etiologies

Most dementias begin insidiously, developing slowly and generally occurring in the elderly age group. The so-called rapidly progressive dementias constitute a different, diverse collection of conditions, many of which are reversible or treatable. For this reason, prompt identification and assessment of acute and subacute forms of dementia are critical to effective treatment. Numerous other entities within this category of presenile rapid-onset dementias are untreatable such as the prion-related diseases. Neuroimaging aids in the diagnosis and evaluation of many of these rapidly progressive dementias, which include myriad conditions ranging from variations of more common neurodegenerative dementias, such as Alzheimer disease, dementia with Lewy bodies, and frontotemporal dementia; infectious-related dementias such as acquired immune deficiency syndrome dementia; autoimmune and malignancy-related conditions; to toxic and metabolic forms of encephalopathy. This first of a 2-part review will specifically address the ability of MR imaging and ancillary neuroimaging strategies to support the diagnostic evaluation of rapidly progressive dementias due to neurodegenerative causes.

Targeting the β secretase BACE1 for Alzheimer's disease therapy

The β secretase, widely known as β-site amyloid precursor protein cleaving enzyme 1 (BACE1), initiates the production of the toxic amyloid β (Aβ) that plays a crucial early part in Alzheimer's disease pathogenesis. BACE1 is a prime therapeutic target for lowering cerebral Aβ concentrations in Alzheimer's disease, and clinical development of BACE1 inhibitors is being intensely pursued. Although BACE1 inhibitor drug development has proven challenging, several promising BACE1 inhibitors have recently entered human clinical trials. The safety and efficacy of these drugs are being tested at present in healthy individuals and patients with Alzheimer's disease, and will soon be tested in individuals with presymptomatic Alzheimer's disease. Although hopes are high that BACE1 inhibitors might be efficacious for the prevention or treatment of Alzheimer's disease, concerns have been raised about potential mechanism-based side-effects of these drugs. The potential of therapeutic BACE1 inhibition might prove to be a watershed in the treatment of Alzheimer's disease.

Network-based biomarkers in Alzheimer's disease: review and future directions

By 2050 it is estimated that the number of worldwide Alzheimer's disease (AD) patients will quadruple from the current number of 36 million people. To date, no single test, prior to postmortem examination, can confirm that a person suffers from AD. Therefore, there is a strong need for accurate and sensitive tools for the early diagnoses of AD. The complex etiology and multiple pathogenesis of AD call for a system-level understanding of the currently available biomarkers and the study of new biomarkers via network-based modeling of heterogeneous data types. In this review, we summarize recent research on the study of AD as a connectivity syndrome. We argue that a network-based approach in biomarker discovery will provide key insights to fully understand the network degeneration hypothesis (disease starts in specific network areas and progressively spreads to connected areas of the initial loci-networks) with a potential impact for early diagnosis and disease-modifying treatments. We introduce a new framework for the quantitative study of biomarkers that can help shorten the transition between academic research and clinical diagnosis in AD.

Cognitive rehabilitation of memory for mild cognitive impairment: a methodological review and model for future research

Several recent reviews have suggested that cognitive rehabilitation may hold promise in the treatment of memory deficits experienced by patients with mild cognitive impairment. In contrast to the previous reviews that mainly focused on outcome, the current review examines key methodological challenges that are critical for designing and interpreting research studies and translating results into clinical practice. Using methodological details from 36 studies, we first examine diagnostic variability and how the use of cutoffs may bias samples toward more severely impaired patients. Second, the strengths and limitations of several common rehabilitative techniques are discussed. Half of the reviewed studies used a multi-technique approach that precludes the causal attribution between any specific technique and subsequent improvement. Third, there is a clear need to examine the dose-response relationship since this information was strikingly absent from most studies. Fourth, outcome measures varied widely and frequently depended on neuropsychological tests with little theoretical justification or ecological relevance. Fifth, we discuss how the variability in each of these other four areas complicates efforts to examine training generalization. Overall, future studies should place greater emphasis on ecologically relevant treatment approaches and outcome measures and we propose a hierarchical model that may aid in this pursuit.

The appropriate use of neuroimaging in the diagnostic work-up of dementia: an evidence-based analysis

BACKGROUND

Diagnosis of dementia is challenging and requires both ruling out potentially treatable underlying causes and ruling in a diagnosis of dementia subtype to manage patients and suitably plan for the future.

OBJECTIVES

This analysis sought to determine the appropriate use of neuroimaging during the diagnostic work-up of dementia, including indications for neuroimaging and comparative accuracy of alternative technologies.

DATA SOURCES

A literature search was performed using Ovid MEDLINE, Ovid MEDLINE In-Process and Other Non-Indexed Citations, Ovid Embase, the Wiley Cochrane Library, and the Centre for Reviews and Dissemination database, for studies published between 2000 and 2013.

REVIEW METHODS

Data on diagnostic accuracy and impact on clinical decision making were abstracted from included studies. Quality of evidence was assessed using GRADE.

RESULTS

The search yielded 5,374 citations and 15 studies were included. Approximately 10% of dementia cases are potentially treatable, though less than 1% reverse partially or fully. Neither prediction rules nor clinical indications reliably select the subset of patients who will likely benefit from neuroimaging. Clinical utility is highest in ambiguous cases or where dementia may be mixed, and lowest for clinically diagnosed Alzheimer disease or clinically excluded vascular dementia. There is a lack of evidence that MRI is superior to CT in detecting a vascular component to dementia. Accuracy of structural imaging is moderate to high for discriminating different types of dementia.

LIMITATIONS

There was significant heterogeneity in estimates of diagnostic accuracy, which often prohibited a statistical summary of findings. The quality of data reported by studies prohibited calculation of likelihood ratios in the present analysis. No studies from primary care were found; thus, generalizability beyond tertiary care settings may be limited.

CONCLUSIONS

A diagnosis of reversible dementia is rare. Imaging has the most clinical utility in cases where there is potentially mixed dementia or ambiguity as to the type of dementia despite prolonged follow-up (e.g., 2 years or more). Both CT and MRI are useful for detecting a vascular component of dementia.

The nature, significance, and glucagon-like peptide-1 analog treatment of brain insulin resistance in Alzheimer's disease

Alzheimer's disease (AD) is an age-related neurodegenerative disease leading over the course of decades to the most common form of dementia. Many of its pathologic features and cognitive deficits may be due in part to brain insulin resistance recently demonstrated in the insulin receptor→insulin receptor substrate-1 (IRS-1) signaling pathway. The proximal cause of such resistance in AD dementia and amnestic mild cognitive impairment (aMCI) appears to be serine inhibition of IRS-1, a phenomenon likely due to microglial release of inflammatory cytokines triggered by oligomeric Aβ. Studies on animal models of AD and on human brain tissue from MCI cases at high risk of AD dementia have shown that brain insulin resistance and many other pathologic features and symptoms of AD may be greatly reduced or even reversed by treatment with FDA-approved glucagon-like peptide-1 (GLP-1) analogs such as liraglutide (Victoza). These findings call attention to the need for further basic, translational, and clinical studies on GLP-1 analogs as promising AD therapeutics.

Online Learning for Classification of Alzheimer Disease based on Cortical Thickness and Hippocampal Shape Analysis

OBJECTIVES

Mobile healthcare applications are becoming a growing trend. Also, the prevalence of dementia in modern society is showing a steady growing trend. Among degenerative brain diseases that cause dementia, Alzheimer disease (AD) is the most common. The purpose of this study was to identify AD patients using magnetic resonance imaging in the mobile environment.

METHODS

We propose an incremental classification for mobile healthcare systems. Our classification method is based on incremental learning for AD diagnosis and AD prediction using the cortical thickness data and hippocampus shape. We constructed a classifier based on principal component analysis and linear discriminant analysis. We performed initial learning and mobile subject classification. Initial learning is the group learning part in our server. Our smartphone agent implements the mobile classification and shows various results.

RESULTS

With use of cortical thickness data analysis alone, the discrimination accuracy was 87.33% (sensitivity 96.49% and specificity 64.33%). When cortical thickness data and hippocampal shape were analyzed together, the achieved accuracy was 87.52% (sensitivity 96.79% and specificity 63.24%).

CONCLUSIONS

In this paper, we presented a classification method based on online learning for AD diagnosis by employing both cortical thickness data and hippocampal shape analysis data. Our method was implemented on smartphone devices and discriminated AD patients for normal group.

Communication Difficulty and Relevant Interventions in Mild Cognitive Impairment: Implications for Neuroplasticity

Mild Cognitive Impairment (MCI) represents a critical point for controlling cognitive decline. Patterns of communication difficulty have been observed in patients with MCI and warrant examination and management. The present systematic review examined (1) characteristics of communication difficulty in MCI by focusing on two domains: expressive and receptive communication, and (2) cognitive interventions that addressed communication difficulties in individuals with MCI. Of the 28 observational studies we reviewed, expressive and receptive communications were generally impaired in individuals with MCI, compared to their healthy counterparts. However, only one of seven interventions effectively improved communication related outcomes. We finished the paper with a discussion about how neuroplasticity influences communication abilities in individuals with MCI to inform the future development of interventions for communication difficulty.

Transcranial direct current stimulation modulates activation and effective connectivity during spatial navigation

BACKGROUND

Allocentric navigation declines with age and neurologic disease whereas egocentric navigation does not; differences that likely arise from maladaptive changes in brain regions mediating spatial (parietal cortex; hippocampus) but not procedural processing (caudate nucleus). Transcranial direct current stimulation (tDCS) holds promise for treating such decline given its ability to modulate neuronal excitability, but its effects have yet to be examined on spatial navigation.

OBJECTIVES/HYPOTHESES

Using healthy young adults as a model, Study 1 intended to validate a novel spatial navigation paradigm using functional magnetic resonance imaging (fMRI). Using these data to determine targets for tDCS, Study 2 aimed to determine if 1) stimulation modulates activation in a polarity-specific manner; 2) stimulation results in global and/or task-specific activation changes; 3) activation changes are accompanied by changes in effective connectivity.

METHODS

All participants underwent fMRI while learning allocentric and egocentric environments. Twelve participants completed Study 1. In Study 2, 16 participants were randomized to 20 min of tDCS (2 mA) using a montage with the anode over PZ and cathode over AF4 (P+F-) or the reverse montage (P-F+).

RESULTS

Study 1 revealed that distinct networks preferentially mediate allocentric and egocentric navigation. Study 2 revealed polarity-dependent changes in activation and connectivity. The P+F- montage increased these measures in spatial regions, especially during allocentric navigation, and the caudate nucleus. Conversely, the P-F+ montage increased activation and connectivity in lateral prefrontal cortices and posterior hippocampus.

CONCLUSIONS

These findings support the neuromodulatory effects of tDCS in non-motor areas and demonstrate proof-of-principle for ameliorating age- and disease-related decline in navigational abilities.

The role of diffusion tensor imaging in detecting microstructural changes in prodromal Alzheimer's disease

The MRI technique diffusion tensor imaging (DTI) is reviewed along with microstructural changes associated with prodromal Alzheimer's disease (AD) as a potential biomarker for clinical applications. The prodromal stage of AD is characterized by mild cognitive impairment (MCI), representing a transitional state between normal aging and AD. Microstructural abnormalities on DTI are promising in vivo biomarkers of gray and white matter changes associated with the progression of AD pathology. Elevated mean diffusivity and decreased fractional anisotropy are consistently found in prodromal AD, and even in cognitively normal elderly who progress to MCI. However, quality of parameter maps may be affected by artifacts of motion, susceptibility, and eddy current-induced distortions. The DTI maps are typically analyzed by region-of-interest or voxel-based analytic techniques such as tract-based spatial statistics. DTI-based index of diffusivity is complementary to macrostructural gray matter changes in the hippocampus in detecting prodromal AD. Breakdown of structural connectivity measured with DTI may impact cognitive performance during early AD. Furthermore, assessment of hippocampal connections may help in understanding the cerebral organization and remodeling associated with treatment response.

Clinical and research applications of simultaneous positron emission tomography and MRI

Evaluation of the molecular processes responsible for disease pathogenesis and progression represents the new frontier of clinical radiology. Multimodality imaging lies at the cutting edge, combining the power of MRI for tissue characterization, microstructural appraisal and functional assessment together with new positron emission tomography (PET) tracers designed to target specific metabolic processes. The recent commercial availability of an integrated clinical whole-body PET-MRI provides a hybrid platform for exploring and exploiting the synergies of multimodal imaging. First experiences on the clinical and research application of hybrid PET-MRI are emerging. This article reviews the rapidly evolving field and speculates on the potential future direction.

White matter abnormalities associated with Alzheimer's disease and mild cognitive impairment: a critical review of MRI studies

In this article, the authors aim to present a critical review of recent MRI studies addressing white matter (WM) abnormalities in Alzheimer's disease (AD) and mild cognitive impairment (MCI), by searching PubMed and reviewing MRI studies evaluating subjects with AD or MCI using WM volumetric methods, diffusion tensor imaging and assessment of WM hyperintensities. Studies have found that, compared with healthy controls, AD and MCI samples display WM volumetric reductions and diffusion tensor imaging findings suggestive of reduced WM integrity. These changes affect complex networks relevant to episodic memory and other cognitive processes, including fiber connections that directly link medial temporal structures and the corpus callosum. Abnormalities in cortico-cortical and cortico-subcortical WM interconnections are associated with an increased risk of progression from MCI to dementia. It can be concluded that WM abnormalities are detectable in early stages of AD and MCI. Degeneration of WM networks causes disconnection among neural cells and the degree of such changes is related to cognitive decline.

Emerging biomarkers in cognition

Knowledge of aging and dementia is rapidly evolving with the aim of identifying individuals in the earliest stages of disease processes. Biomarkers allow clinicians to show the presence of a pathologic process and resultant synapse dysfunction and neurodegeneration, even in the earliest stages. This article focuses on biomarkers for mild cognitive impairment caused by Alzheimer disease, structural magnetic resonance imaging, fluorodeoxyglucose positron emission tomography (PET) or single-photon emission computed tomography, and PET with dopamine ligands. Although these biomarkers are useful, several limitations exist. Several new biomarkers are emerging and a more biological characterization of underlying pathophysiologic spectra may become possible.

An expanded role for neuroimaging in the evaluation of memory impairment

SUMMARY

Alzheimer disease affects millions of people worldwide. The neuropathologic process underlying this disease begins years, if not decades, before the onset of memory decline. Recent advances in neuroimaging suggest that it is now possible to detect Alzheimer-associated neuropathologic changes well before dementia onset. Here, we evaluate the role of recently developed in vivo biomarkers in the clinical evaluation of Alzheimer disease. We discuss how assessment strategies might incorporate neuroimaging markers to better inform patients, families, and clinicians when memory impairment prompts a search for diagnosis and management options.

White matter hyperintensities and amyloid are independently associated with entorhinal cortex volume among individuals with mild cognitive impairment

BACKGROUND

Current hypothetical models of Alzheimer's disease (AD) pathogenesis emphasize the role of β-amyloid (Aβ), tau deposition, and neurodegenerative changes in the mesial temporal lobe, particularly the entorhinal cortex and hippocampus. However, many individuals with clinical AD who come to autopsy also exhibit cerebrovascular disease. The relationship between AD and vascular pathology is unclear, especially whether they represent additive and independent effects on neuronal injury. We used data from the Alzheimer's Disease Neuroimaging Initiative (ADNI) to (1) confirm whether entorhinal cortex and hippocampal volume are associated with memory among individuals with amnestic mild cognitive impairment (MCI) who are at risk for AD; and (2) determine whether regional white matter hyperintensity (WMH) volume, a radiological marker of small-vessel cerebrovascular disease, is associated with entorhinal cortex and hippocampal volume independent of putative AD biomarkers in this group.

METHODS

Cognitive test scores, entorhinal cortex volume, hippocampus volume, intracranial volume, and cerebrospinal fluid-derived phosphorylated tau and Aβ1-42 protein levels were measured in 199 subjects with amnestic MCI (mean age = 74.89 ± 7.47). Lobar WMH volumes were derived from T1-, proton-density-, and T2-weighted magnetic resonance imaging scans. We examined the association between entorhinal cortex volume and cognition. Next, we examined the association of tau and Aβ1-42 with entorhinal cortex volume and between lobar WMH and entorhinal cortex volume. Finally, tau, Aβ1-42, and regional WMH volumes were entered simultaneously to predict entorhinal cortex volume. We repeated the analyses with hippocampal volume instead of entorhinal cortex volume. The analyses were also repeated with the sample restricted to those MCI patients who transitioned to AD on subsequent ADNI follow-up visits (n = 86).

RESULTS

Larger entorhinal cortex volume was associated with better memory but not with performance on a task of executive functioning. Lower levels of Aβ1-42 and higher temporal WMH volumes were associated with smaller entorhinal cortex volume. When entered simultaneously, temporal lobe WMH volume was more reliably associated with entorhinal cortex volume than was Aβ1-42. The findings were similar for hippocampus volume and when the sample was restricted to MCI patients who subsequently transitioned to AD.

CONCLUSIONS

The findings confirm the role of entorhinal cortex and hippocampus volume in influencing memory decline in amnestic MCI, and emphasize that even in this nominally AD prodromal condition, WMH may be influencing regional neurodegeneration.

Multivariate classification of blood oxygen level-dependent FMRI data with diagnostic intention: a clinical perspective

SUMMARY

There has been a recent upsurge of reports about applications of pattern-recognition techniques from the field of machine learning to functional MR imaging data as a diagnostic tool for systemic brain disease or psychiatric disorders. Entities studied include depression, schizophrenia, attention deficit hyperactivity disorder, and neurodegenerative disorders like Alzheimer dementia. We review these recent studies which-despite the optimism from some articles-predominantly constitute explorative efforts at the proof-of-concept level. There is some evidence that, in particular, support vector machines seem to be promising. However, the field is still far from real clinical application, and much work has to be done regarding data preprocessing, model optimization, and validation. Reporting standards are proposed to facilitate future meta-analyses or systematic reviews.

CSF Aβ1-42 combined with neuroimaging biomarkers in the early detection, diagnosis and prediction of Alzheimer's disease

The development of validated, qualified, and standardized biomarkers for Alzheimer's disease (AD) that allow for an early presymptomatic diagnosis and discrimination (classification) from other types of dementia and neurodegenerative diseases is warranted to accelerate the successful development of novel disease-modifying therapies. Here, we focus on the value of the 42-residue-long amyloid β isoform (Aβ1-42) peptide in the cerebrospinal fluid as the core, feasible neurobiochemical marker for the amyloidogenic mechanisms in early-onset familial and late-onset sporadic AD. We discuss the role and use of Aβ1-42 in combination with evolving neuroimaging biomarkers in AD detection and diagnosis. Multimodal neuroimaging techniques, directly providing structural-functional-metabolic aspects of brain pathophysiology, are supportive to predict and monitor the progression of the disease. Advances in multimodal neuroimaging provide new insights into brain organization and enable the detection of specific proteins and/or protein aggregates associated with AD. The combination of biomarkers from different methodologies is believed to be of incrementally added risk-value to accurately identify asymptomatic and prodromal individuals who will likely progress to dementia and represent rational biomarker candidates for preventive and symptomatic pharmacological intervention trials.

MicroRNA in Alzheimer's disease: an exploratory study in brain, cerebrospinal fluid and plasma

MicroRNA (miRNA) may be potential biomarkers of Alzheimer's disease (AD). The objective of this investigation was to demonstrate that miRNAs in human brain or biofluids are differentially expressed according to disease status, tissue type, neuritic plaque score or Braak stage. Post-mortem brain (PMB) miRNA were profiled using arrays and validated using quantitative RT-PCR (qRT-PCR). Five qRT-PCR-validated miRNAs were measured in an independent sample of PMB, cerebrospinal fluid and plasma from the same subjects. Plasma miR-15a was found to be associated with plaque score in the independent sample. In conclusion, miRNA present in human biofluids may offer utility as biomarkers of AD.

Brain investigation and brain conceptualization

The brain of a patient with Alzheimer's disease (AD) undergoes changes starting many years before the development of the first clinical symptoms. The recent availability of large prospective datasets makes it possible to create sophisticated brain models of healthy subjects and patients with AD, showing pathophysiological changes occurring over time. However, these models are still inadequate; representations are mainly single-scale and they do not account for the complexity and interdependence of brain changes. Brain changes in AD patients occur at different levels and for different reasons: at the molecular level, changes are due to amyloid deposition; at cellular level, to loss of neuron synapses, and at tissue level, to connectivity disruption. All cause extensive atrophy of the whole brain organ. Initiatives aiming to model the whole human brain have been launched in Europe and the US with the goal of reducing the burden of brain diseases. In this work, we describe a new approach to earlier diagnosis based on a multimodal and multiscale brain concept, built upon existing and well-characterized single modalities.

Testosterone effect on brain metabolism in elderly patients with Alzheimer's disease: comparing two cases at different disease stages

OBJECTIVE

To describe the effect of testosterone replacement therapy (TRT) on the brain activity of two demented, hypogonadal male patients with early and late-stage Alzheimer's disease (AD), respectively.

METHODS

We describe the clinical and positron emission tomography (PET) findings for two individuals, one with early stage and the other with late-stage Alzheimer's disease, before and after treatment with a topical testosterone gel. Both patients were hypogonadal at baseline. We assessed cerebral glucose metabolism (CGM) via (18)F-fluorodeoxyglucose (FDG)-positron emission tomography (PET). We investigated whether there are testosterone-susceptible areas within cerebral structures in patients with Alzheimer's disease.

RESULTS

Under testosterone replacement therapy, changes in cerebral glucose metabolism were observed in both patients. Improvement in glucose uptake was observed most consistently in the parietal lobe and brainstem; decreased glucose metabolism was observed in the temporal lobe, the limbic system and the insula for these two subjects.

DISCUSSION

These case reports demonstrate the potential for PET scanning to detect changes in cerebral glucose metabolism in hypogonadal men with Alzheimer's disease who are treated with testosterone. Further study will be needed to investigate the consistency and significance of these changes in terms of magnitude and brain region, and the correlation with functional changes.

Functional MRI and neural responses in a rat model of Alzheimer's disease

Based on the hypothesis that brain plaques and tangles can affect cortical function in Alzheimer's disease (AD), we investigated functional responses in an AD rat model (called the Samaritan Alzheimer's rat achieved by ventricular infusion of amyloid peptide) and age-matched healthy control. High-field functional magnetic resonance imaging (fMRI) and extracellular neural activity measurements were applied to characterize sensory-evoked responses. Electrical stimulation of the forepaw led to BOLD and neural responses in the contralateral somatosensory cortex and thalamus. In AD brain we noted much smaller BOLD activation patterns in the somatosensory cortex (i.e., about 50% less activated voxels compared to normal brain). While magnitudes of BOLD and neural responses in the cerebral cortex were markedly attenuated in AD rats compared to normal rats (by about 50%), the dynamic coupling between the BOLD and neural responses in the cerebral cortex, as assessed by transfer function analysis, remained unaltered between the groups. However thalamic BOLD and neural responses were unaltered in AD brain compared to controls. Thus cortical responses in the AD model were indeed diminished compared to controls, but the thalamic responses in the AD and control rats were quite similar. Therefore these results suggest that Alzheimer's disease may affect cortical function more than subcortical function, which may have implications for interpreting altered human brain functional responses in fMRI studies of Alzheimer's disease.

Neuroimaging insights into network-based neurodegeneration

PURPOSE OF REVIEW

Convergent evidence from a number of neuroscience disciplines supports the hypothesis that Alzheimer's disease and other neurodegenerative disorders progress along brain networks. This review considers the role of neuroimaging in strengthening the case for network-based neurodegeneration and elucidating potential mechanisms.

RECENT FINDINGS

Advances in functional and structural MRI have recently enabled the delineation of multiple large-scale distributed brain networks. The application of these network-imaging modalities to neurodegenerative disease has shown that specific disorders appear to progress along specific networks. Recent work applying theoretical measures of network efficiency to in-vivo network imaging has allowed for the development and evaluation of models of disease spread along networks. Novel MRI acquisition and analysis methods are paving the way for in-vivo assessment of the layer-specific microcircuits first targeted by neurodegenerative diseases. These methodological advances coupled with large, longitudinal studies of subjects progressing from healthy aging into dementia will enable a detailed understanding of the seeding and spread of these disorders.

SUMMARY

Neuroimaging has provided ample evidence that neurodegenerative disorders progress along brain networks, and is now beginning to elucidate how they do so.

Use of proteomic methods in the analysis of human body fluids in Alzheimer research

Proteomics is the study of the entire population of proteins and peptides in an organism or a part of it, such as a cell, tissue, or fluids like cerebrospinal fluid, plasma, serum, urine, or saliva. It is widely assumed that changes in the composition of the proteome may reflect disease states and provide clues to its origin, eventually leading to targets for new treatments. The ability to perform large-scale proteomic studies now is based jointly on recent advances in our analytical methods. Separation techniques like CE and 2DE have developed and matured. Detection methods like MS have also improved greatly in the last 5 years. These developments have also driven the fields of bioinformatics, needed to deal with the increased data production and systems biology. All these developing methods offer specific advantages but also come with certain limitations. This review describes the different proteomic methods used in the field, their limitations, and their possible pitfalls. Based on a literature search in PubMed, we identified 112 studies that applied proteomic techniques to identify biomarkers for Alzheimer disease. This review describes the results of these studies on proteome changes in human body fluids of Alzheimer patients reviewing the most important studies. We extracted a list of 366 proteins and peptides that were identified by these studies as potential targets in Alzheimer research.

Genetic susceptibility testing for neurodegenerative diseases: ethical and practice issues

As the genetics of neurodegenerative disease become better understood, opportunities for genetic susceptibility testing for at-risk individuals will increase. Such testing raises important ethical and practice issues related to test access, informed consent, risk estimation and communication, return of results, and policies to prevent genetic discrimination. The advent of direct-to-consumer genetic susceptibility testing for various neurodegenerative disorders (including Alzheimer's disease (AD), Parkinson's disease, and certain prion diseases) means that ethical and practical challenges must be faced not only in traditional research and clinical settings, but also in broader society. This review addresses several topics relevant to the development and implementation of genetic susceptibility tests across research, clinical, and consumer settings; these include appropriate indications for testing, the implications of different methods for disclosing test results, clinical versus personal utility of risk information, psychological and behavioral responses to test results, testing of minors, genetic discrimination, and ethical dilemmas posed by whole-genome sequencing. We also identify future areas of likely growth in the field, including pharmacogenomics and genetic screening for individuals considering or engaged in activities that pose elevated risk of brain injury (e.g., football players, military personnel). APOE gene testing for risk of Alzheimer's disease is used throughout as an instructive case example, drawing upon the authors' experience as investigators in a series of multisite randomized clinical trials that have examined the impact of disclosing APOE genotype status to interested individuals (e.g., first-degree relatives of AD patients, persons with mild cognitive impairment).

Two-year course of cognitive function and instrumental activities of daily living in older adults with bipolar disorder: evidence for neuroprogression?

BACKGROUND

While bipolar disorder (BD) is a leading cause of disability, and an important contributor to disability in BD is cognitive impairment, there is little systematic research on the longitudinal course of cognitive function and instrumental activities of daily living (IADLs) in late-life. In this report, we characterize the 2-year course of cognitive function and IADLs in older adults with BD. Method We recruited non-demented individuals 50 years and older with BD I or BD II (n = 47) from out-patient clinics or treatment studies at the University of Pittsburgh. Comparator subjects ('controls') were 22 individuals of comparable age and education with no psychiatric or neurologic history, but similar levels of cardiovascular disease. We assessed cognitive function and IADLs at baseline, 1- and 2-year time-points. The neuropsychological evaluation comprised 21 well-established and validated tests assessing multiple cognitive domains. We assessed IADLs using a criterion-referenced, performance-based instrument. We employed repeated-measures mixed-effects linear models to examine trajectory of cognitive function. We employed non-parametric tests for analysis of IADLs.

RESULTS

The BD group displayed worse cognitive function in all domains and worse IADL performance than the comparator group at baseline and over follow-up. Global cognitive function and IADLs were correlated at all time-points. The BD group did not exhibit accelerated cognitive decline over 2 years.

CONCLUSIONS

Over 2 years, cognitive impairment and associated functional disability of older adults with BD appear to be due to long-standing neuroprogressive processes compounded by normal cognitive aging rather than accelerated cognitive loss in old age.

Clinical utility and analytical challenges in measurement of cerebrospinal fluid amyloid-β(1-42) and τ proteins as Alzheimer disease biomarkers

BACKGROUND

Over the past 2 decades, clinical studies have provided evidence that cerebrospinal fluid (CSF) amyloid β(1-42) (Aβ(1-42)), total τ (t-τ), and τ phosphorylated at Thr181 (p-τ(181)) are reliable biochemical markers of Alzheimer disease (AD) neuropathology.

CONTENT

In this review, we summarize the clinical performance and describe the major challenges for the analytical performance of the most widely used immunoassay platforms [based on ELISA or microbead-based multianalyte profiling (xMAP) technology] for the measurement of CSF AD biomarkers (Aβ(1-42), t-τ, and p-τ(181)). With foundational immunoassay data providing the diagnostic and prognostic values of CSF AD biomarkers, the newly revised criteria for the diagnosis of AD include CSF AD biomarkers for use in research settings. In addition, it has been suggested that the selection of AD patients at the predementia stage by use of CSF AD biomarkers can improve the statistical power of clinical trial design. Owing to the lack of a replenishable and commutable human CSF-based standardized reference material (SRM) and significant differences across different immunoassay platforms, the diagnostic-prognostic cutpoints of CSF AD biomarker concentrations are not universal at this time. These challenges can be effectively met in the future, however, through collaborative ongoing standardization efforts to minimize the sources of analytical variability and to develop reference methods and SRMs.

SUMMARY

Measurements of CSF Aβ(1-42), t-τ, and p-τ(181) with analytically qualified immunoassays reliably reflect the neuropathologic hallmarks of AD in patients at the early predementia stage of the disease and even in presymptomatic patients. Thus these CSF biomarker tests are useful for early diagnosis of AD, prediction of disease progression, and efficient design of drug intervention clinical trials.

Clinical applications of functional MR imaging

Functional magnetic resonance (fMR) imaging for neurosurgical planning has become the standard of care in centers where it is available. Although paradigms to measure eloquent cortices are not yet standardized, simple tasks elicit reliable maps for planning neurosurgical procedures. A patient-specific paradigm design will refine the usability of fMR imaging for prognostication and recovery of function. Certain pathologic conditions and technical issues limit the interpretation of fMR imaging maps in clinical use and should be considered carefully. However, fMR imaging for neurosurgical planning continues to provide insights into how the brain works and how it responds to pathologic insults.

Physical activity and brain function in older adults at increased risk for Alzheimer's disease

Leisure-time physical activity (PA) and exercise training are known to help maintain cognitive function in healthy older adults. However, relatively little is known about the effects of PA on cognitive function or brain function in those at increased risk for Alzheimer's disease through the presence of the apolipoproteinE epsilon4 (APOE-ε4) allele, diagnosis of mild cognitive impairment (MCI), or the presence of metabolic disease. Here, we examine the question of whether PA and exercise interventions may differentially impact cognitive trajectory, clinical outcomes, and brain structure and function among individuals at the greatest risk for AD. The literature suggests that the protective effects of PA on risk for future dementia appear to be larger in those at increased genetic risk for AD. Exercise training is also effective at helping to promote stable cognitive function in MCI patients, and greater cardiorespiratory fitness is associated with greater brain volume in early-stage AD patients. In APOE-ε4 allele carriers compared to non-carriers, greater levels of PA may be more effective in reducing amyloid burden and are associated with greater activation of semantic memory-related neural circuits. A greater research emphasis should be placed on randomized clinical trials for exercise, with clinical, behavioral, and neuroimaging outcomes in people at increased risk for AD.

Relationship between genetic risk factors and markers for Alzheimer's disease pathology

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by neuritic plaques (main constituent: β-amyloid [Aβ]) and neurofibrillary tangles (hyperphosphorylated tau protein) in the brain. Abnormalities in Aβ and tau can be measured upon neuropathological examination, in cerebrospinal fluid or by PET. Etiologically, a growing body of evidence suggests that susceptibility to AD is genetically controlled. However, the precise nature of the underlying risk genes and their relation to AD biomarkers remains largely elusive. To this end, we performed a qualitative review of 17 studies (covering 47 polymorphisms in 26 genes) and investigated the potential relation between the most compelling AD risk genes and markers for Aβ and tau in cerebrospinal fluid, PET imaging and neuropathological examination. Of all covered genes, only APOE and PICALM showed consistent effects on Aβ but not on tau, while no obvious effects were observed for CLU, CR1, ACE, SORL and MAPT.

Isotropic anomalous filtering in Diffusion-Weighted Magnetic Resonance Imaging

Noise is inherent to Diffusion-Weighted Magnetic Resonance Imaging (DWI) and noise reduction methods are necessary. Although process based on classical diffusion is one of the most used approaches for digital image, anomalous diffusion has the potential for image enhancement and it has not been tested for DWI noise reduction. This study evaluates Anomalous Diffusion (AD) filter as DWI enhancement method. The proposed method was applied to magnetic resonance diffusion weighted images (DW-MRI) with different noise levels. Results show better performance for anomalous diffusion when compared to classical diffusion approach. The proposed method has shown potential in DWI enhancement and can be an important process to improve quality in DWI for neuroimage-based diagnosis.

In vivo 1H magnetic resonance spectroscopy in young-adult daily marijuana users

To date, there has been little work describing the neurochemical profile of young, heavy marijuana users. In this study, we examined 27 young-adult marijuana users and 26 healthy controls using single-voxel magnetic resonance spectroscopy on a 3 T scanner. The voxel was placed in the dorsal striatum, and estimated concentrations of glutamate + glutamine, myo-inositol, taurine + glucose, total choline and total N-acetylaspartate were examined between groups. There were no overall group effects, but two metabolites showed group by sex interactions. Lower levels of glutamate + glutamine (scaled to total creatine) were observed in female, but not male, marijuana users compared to controls. Higher levels of myo-inositol were observed in female users compared to female non-users and to males in both groups. Findings are discussed in relation to patterns of corticostriatal connectivity and function, in the context of marijuana abuse.

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The neurochemical profile of the basal ganglia was examined in young marijuana users.

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Glutamate/glutamine levels were lower in female users versus male users and controls.

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Higher myo-inositol levels were observed in female users as compared to other groups.

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Neurochemical impacts of marijuana may be particularly pronounced in females.

A cross-sectional study on cerebrospinal fluid biomarker levels in cognitively normal elderly subjects with or without a family history of Alzheimer's disease

BACKGROUND

Cerebrospinal fluid (CSF) biomarkers reflect changes in the brain, and contribute to early screening. Maternal inheritance is putatively stronger than paternal inheritance for late-onset Alzheimer's disease (LOAD).

METHODS

Clinical data of 162 cognitively normal subjects were reviewed. A standard questionnaire was used to identify LOAD family history. Mini-mental state examination (MMSE) was used to evaluate cognition. CSF Aβ1-40, Aβ1-42, total and phosphorylated tau were measured using ELISA.

AIMS

To compare biomarkers in cognitively normal elderly subjects with versus without LOAD family history.

RESULTS

Among the 162 subjects, 38 and 60 had LOAD family history on paternal and maternal sides, respectively. The remaining 60 subjects had no family history. No difference was noted in age, gender, education level, MMSE score, and memory impairment complaint in the three groups. Aβ42 and the Aβ42/40 ratio were lower than in subjects with a maternal history than in subjects with a paternal history or without family history (P < 0.05 in both). Phosphorylated and total tau did not differ among the three groups.

CONCLUSION

Offspring with a family history of LOAD on the maternal side have lower Aβ42 and Aβ42/40 ratio in the CSF, and maybe at higher risk for developing AD.

Development of biomarkers to chart all Alzheimer's disease stages: the royal road to cutting the therapeutic Gordian Knot

The aim of this perspective article is to stimulate radical shifts in thinking and foster further discussion on the effective discovery, development, validation, and qualification process of biological markers derived from all available technical modalities that meet the complex conceptual and pathophysiological challenges across all stages of the complex, nonlinear, dynamic, and chronically progressive sporadic Alzheimer's disease (AD). This perspective evaluates the current state of the science regarding a broad spectrum of hypothesis-driven and exploratory technologies and "markers" as candidates for all required biomarker functions, in particular, surrogate indicators of adaptive to maladaptive and compensatory to decompensatory, reversible to irreversible brain "systems failure." We stress the future importance of the systems biology (SB) paradigm (next to the neural network paradigm) for substantial progress in AD research. SB represents an integrated and deeper investigation of interacting biomolecules within cells and organisms. This approach has only recently become feasible as high-throughput technologies and mass spectrometric analyses of proteins and lipids, together with rigorous bioinformatics, have evolved. Existing high-content data derived from clinically and experimentally derived neural tissues point to convergent pathophysiological pathways during the course of AD, transcending traditional descriptive studies to reach a more integrated and comprehensive understanding of AD pathophysiology, derived systems biomarkers, and "druggable" system nodes. The discussion is continued on the premise that the lack of integration of advanced biomarker technologies and transfertilization from more mature translational research fields (e.g., oncology, immunology, cardiovascular), which satisfy regulatory requirements for an accurate, sensitive, and well-validated surrogate marker of specific pathophysiological processes and/or clinical outcomes, is a major rate-limiting factor for the successful development and approval of effective treatments for AD prevention. We consider the conceptual, scientific, and technical challenges for the discovery-development-validation-qualification process of biomarker tools and analytical algorithms for detection of the earliest pathophysiological processes in asymptomatic individuals at elevated risk during preclinical stages of AD. The most critical need for rapid translation of putative markers into validated (performance) and standardized (harmonized standard operating procedures) biomarker tools that fulfill regulatory requirements (qualify for use in treatment trials: e.g., safety, target engagement, mechanism of action, enrichment, stratification, secondary and primary outcome, surrogate outcome) is the availability of a large-scale worldwide comprehensive longitudinal database that includes the following cohorts: (a) healthy aging, (b) people at elevated risks (genetic/epigenetic/lifestyle/comorbid conditions), and (c) asymptomatic-preclinical/prodromal-mild cognitive impairment/syndromal mild, moderate, or severe AD. Our proposal, as initial strategic steps for integrating markers into future development of diagnostic and therapy trial technologies, is to work toward: (a) creating the essential research and development infrastructure as an international shared resource, (b) building the organizational structure for managing such a multinational shared resource, and (c) establishing an integrated transsectoral multidisciplinary global network of collaborating investigators to help build and use the shared research resource.

Neuroimaging in dementias

PURPOSE OF REVIEW

To critically review data on the use of neuroimaging tools in the clinical diagnostic investigation of dementias.

RECENT FINDINGS

For many years, the use of neuroimaging tools in the evaluation of dementias has been restricted to excluding neurosurgical lesions that may account for the cognitive decline. However, modern neuroimaging extends beyond this traditional role of excluding other conditions and has a key role in the clinical investigation of Alzheimer's disease and of other degenerative cortical dementias. MRI, PET with fluorodeoxyglucose, and single-photon emission computed tomography are topographic markers of neural damage and enable the identification of specific lesional patterns that characterize Alzheimer's disease and other cortical dementias. More recently, PET amyloid markers have enabled the in-vivo assessment of amyloid load, a key feature in the physiopathology of Alzheimer's disease.

SUMMARY

The combined use of neuroimaging examinations with clinical, neuropsychological, and cerebrospinal fluid markers can improve the specificity of the diagnosis of Alzheimer's disease, even at early stages of the disease. In the following years, progress in research will provide standardized and validated imaging markers of Alzheimer's disease and other dementias, which may increase their application in clinical settings.

Enrichment and stratification for predementia Alzheimer disease clinical trials

The tau and amyloid pathobiological processes underlying Alzheimer disease (AD) progresses slowly over periods of decades before clinical manifestation as mild cognitive impairment (MCI), then more rapidly to dementia, and eventually to end-stage organ failure. The failure of clinical trials of candidate disease modifying therapies to slow disease progression in patients already diagnosed with early AD has led to increased interest in exploring the possibility of early intervention and prevention trials, targeting MCI and cognitively healthy (HC) populations. Here, we stratify MCI individuals based on cerebrospinal fluid (CSF) biomarkers and structural atrophy risk factors for the disease. We also stratify HC individuals into risk groups on the basis of CSF biomarkers for the two hallmark AD pathologies. Results show that the broad category of MCI can be decomposed into subsets of individuals with significantly different average regional atrophy rates. By thus selectively identifying individuals, combinations of these biomarkers and risk factors could enable significant reductions in sample size requirements for clinical trials of investigational AD-modifying therapies, and provide stratification mechanisms to more finely assess response to therapy. Power is sufficiently high that detecting efficacy in MCI cohorts should not be a limiting factor in AD therapeutics research. In contrast, we show that sample size estimates for clinical trials aimed at the preclinical stage of the disorder (HCs with evidence of AD pathology) are prohibitively large. Longer natural history studies are needed to inform design of trials aimed at the presymptomatic stage.

Classification of mild cognitive impairment and Alzheimer disease using model-based MR and magnetization transfer imaging

BACKGROUND AND PURPOSE

Early stratification of degenerative processes is a prerequisite to warrant therapeutic options in prodromal Alzheimer disease. Our aim was to investigate differences in cerebral macromolecular tissue composition between patients with AD, mild cognitive impairment, and age- and sex-matched healthy controls by using model-based magnetization transfer with a binary spin-bath magnetization transfer model and magnetization transfer ratio at 1.5 T.

MATERIALS AND METHODS

We investigated patients with de novo AD (n=18), MCI (n=18), and CTRLs (n=18). A region-of-interest analysis of the entorhinal cortex, hippocampal head and body, insula, and temporal neocortex was performed with fuzzy clustering to associate every subregion to a cluster representative for each group.

RESULTS

Cluster analysis achieved a concordance of 0.92 (50 of 54 subjects) between a combination of the calculated mMT parameters (kf,kr,T2r,F,T2f) in the entorhinal cortex and the neuropsychological diagnosis. The sensitivity and specificity for the discrimination of AD from MCI reached 1 and 0.94, with a positive predictive value of 0.95 and a negative predictive value of 1. Compared with mMT, the concordance for MTR was 0.83 (45 of 54 subjects) with a lower specificity of 0.5 and positive predictive value of 0.67 to discriminate patients with AD and MCI.

CONCLUSIONS

mMT imaging detects macromolecule-related alterations and allows an improved classification of patients with early AD and MCI compared with MTR.

Mapping of distributions of a local b-matrix cross-term strength using diffusion tensor MRI in patients with Alzheimer's disease

PURPOSE

Mapping of the distribution of local susceptibility strength could be very important in understanding the mechanisms of progression in neurodegenerative diseases, due to depositions of iron and iron-containing plaques. The goal of this study is to map the voxelwise distribution of local cross-term b-value (b(c)) effect caused by interactions between the external and internal gradients, in subjects with Alzheimer's disease (AD), mild cognitive impairment (MCI), and cognitively normal (CN) elderly, using a diffusion tensor (DT) MRI.

METHODS

Two DT-MRI experiments were conducted with opposite polarities of the external diffusion-sensitizing gradients, and the authors modeled the 3 × 3 tensor matrix of b(c) maps and drove a rotationally independent mean b(c) (i.e., MB(c)) maps. To test whether AD has higher cross-term gradients than MCI and∕or CN, 15 AD patients, 18 MCI patients, and 16 CN controls were acquired from DT-MRI data, with six diffusion encoding directions, five b-values (0, 160, 360, 640, and 1000 s∕mm(2)), and positively and negatively alternating polarities of the external diffusion-sensitizing gradients. The b(c) and MB(c) maps were calculated and were spatially normalized into a study specific template for all subjects. The differences of MB(c) maps across the three subject groups were investigated with voxelwise one-way ANOVA tests for each b-value. The differences of MB(c) maps, among the four b-values, were also investigated with a voxelwise one-way within-subject ANOVA test for each group.

RESULTS

The authors successfully mapped the local cross-term strength, using a DT-MRI data in the three groups. The MB(c) differences between the groups were increased with increasing b-values. Compared with the CN group and the MCI group, MB(c) values in the AD group were significantly increased. However, compared with the CN group, MB(c) values in the MCI group were not significantly different for all the b-values.

CONCLUSIONS

In order to map the b-matrix cross-term effect, the authors developed a rotationally invariant index of MB(c), and the index was applied in AD, MCI, and CN subjects. In the AD group, compared with the MCI and CN groups, MB(c) values were increased. AD patients may have much more local intrinsic gradients in the brain than those MCI or CN subjects. MB(c) maps may be used to detect the intrinsically susceptible materials in the human brain, such as iron-containing plaques in the brain with AD.